Artificial leather manufacture



Patented Apr. 24, 1934 ARTIFICIAL LEATHER MANUFACTURE Milton 0. Schur, Berlin, N. 1]., assignor to Brown Company, Berlin, N. H., a corporation of Maine No Drawing.

21 Claims.

In making artificial leather by the impregnation of porous, felted foundations with aqueous rubber dispersions of the nature of natural or synthetic latex, it has been a long-standing 5 problem to secure a finished sheet. of satisfactory internal ply adhesion, that is, a sheet which iss not easily separated into plies or laminations when split open at its edges. The fact is, that even though one may start with a highly bibulous felt or web which lends itself to quick and uniform impregnation with latex, the dried sheet tends to be poorer in rubber in its interior than on its surface portions. This trouble arises from the fact that during the drying of the impregnated web, the water diffuses to the surface where evaporation is taking place and in so doing tends to carry therewith the colloidalrubber particle. Unless the rubber is used in such excessive amount that the finished sheet 2Q resembles rubber more than leather in the physical properties, the internal ply adhesion is disconcertingly low. This is especiallytrue of artificial leathers wherein a waterlaid web of fibers is used as a base, for, in such a web, there 5 is a tendency for fiber ,stratification, thatis, for the fibers to deposit on the usual forming wire in strata or layers, especially when the fibers are in the comparatively free and unhydrated condition essential to the realization of a soft, absorbent web.

In many connections, it is of fundamental importance that artificial leathers of the foregoing class be made with high internal ply adhesion and without consuming so much rubber as would detract from their leather-like qualities or render their cost of manufacture prohibitively expensive. For instance, when artificial leathers are to serve for such purposes as welt-innersoles, it is a prerequisite that they have high internal ply adhesion in order to withstand the stresses of shoemaking and of wear. It is also a requisite that the desired high internal ply adhesion be reached without the use of excessive rubber, since, otherwise, the innersole will not only be expensive but will tend to burn the feet.

It was reasoned that the migration of rubber particles to the surface of the impregnated web as it is being dried could be avoided by setting or coagulating the rubber in the web before the drying operation. The practical wayin which to apply the coagulant is, however, the next problem. Thus, when the freshly-impregnated web is treated with a coagulant, it is found that unless the coagulant is a potent and Application September 1, 1932, Serial No. 631,368

penetrating one, only the latex on the surface of the web is affected. The use of potent and penetrating coa'gulants, however, such as strong, hot solutions of acetic or sulphurous acid, gives rise to the danger of injuring the fibers and the rubber and of acid residues and offensive odors being left in the finished sheet even though it be washed. It is thus seen that this sort of practice is, at best, attended by many practical difficulties. On the other hand, if one resorts to the introduction of solutions of milder coagulants, such as acid salts; into the web before it receives the latex, other difiiculties spring up. A study of this practice revealed that when the web was uniformly wet with a solution of such coagulants and then treated with latex, the outer pores of the web were prematurely plugged and its interior was badly deficient in rubber. When the web was treated with the coagulant solution and dried before the latex treatment, it was found that owing to the migration of. the coagulant to the surface of the sheet, comparatively large quantities were needed to ensure sufi'icient being left in the center of the sheet. Here, too, it was found that because of the excessive concentration of coagulant on the surface of the Web, the latex was partially or completely coagulated before it had an opportunity of reaching the interior of the web and depositing therein as much rubber as on the exterior.

In accordance with the present invention, the foregoing difficulties are overcome by forming the web or felt in a dry way from a supply of fibers throughout which the coagulant has been uniformly incorporated and then treating the web so made with latex and drying it. I have found that webs so made permit the latex to spread therethrough quickly and uniformly and that only a comparatively small amount of mild coagulant is all that is necessary to inhibit migration of the rubber particles during subsequent drying. The finished product thus contains the rubber properly distributed therethrough and it is of excellent ply adhesion both on this account and on account of the absence of strata or laminae therein even when its rubber content is sufficiently low so that it can compete with genuine leather both in quality and in price for such purposes as weltinnersoles.

In applying the principles of the present invention, one may form the web or felt in a dry way. from different kinds of 'fibers with which the different types of machines. Thus, one may employ a carding machine in connection with such fibers as cotton and/or wool. I have, however, secured excellent results in working with short fibers, such as wood pulps, whose fibers can be separated or individualized in any suitable manner, deposited from suspension in air as a layer or web of the proper weight, compacted to the desired thickness, and impregnated with latex. Because of the smooth and rapid coagulation of latex throughout the web, sufficient wet strength is at once imparted to the web so that, despitethe fact that it is rendered soggy by the latex, it can be drawn progressively through a bath of latex as the impregnating medium and then passed through squeeze rolls with a greatly minimized danger of disintegrating into a slush. The wood pulp serving as raw material is preferably of a highly refined or purified character, as such wood pulp conduces to high softness and absorbency in the webs and excellent pliancy in the finished artificial leather. It may be treated in either wet or dry condition with the rubber coagulant, so long as it is then dried and otherwise properly conditioned for the web-forming operation.

As an example of procedure, I may start with so-called drier sheets of highly purified wood cellulose as my base fiber. These sheets may be dipped in a dilute solution of suitable rubbercoagulant, preferably magnesium chloride, and then squeezed until they contain about 1% magnesium chloride, based on the weight of fiber. The sheets may then be redried as in a hot-air oven and delivered to a hammer mill, a picker, or other suitable machine designed to reduce the sheets to a fluffy mass of separate or individual fiber units. The fiber units may then be lifted from the mass in an air current induced by a blower or suction fan and directed against a moving screen or other foraminous conveyor on which deposition of the fiber is allowed to take place until a web or felt of the desired weight, say, 0.8 pounds per square yard, is had. The web may be progressively formed inthis way, compacted as by press rolls to a thickness of, say, 50 mils, conducted through a bath of latex of the desired solids content, and thence through a hot-air drier. In the event that the finished artificial leather is to serve for such uses as shoe innersoles, the bath of latex may be one containing about 32%. solids and the web passed therethrough may be squeezed to a rubber content of about 50% to before it enters the dryer. The resulting dry sheet has remarkably high internal ply adhesion and is admirably adapted for use as welt-innersole material. For such use, the sheet may be stiffened to advantage with a suitable secondary impregnant. Thus, it may be passed through a solution of a resin, natural or synthetic, and then dried, or through a bath of molten thermoplastic material which is permitted to congeal in the pores and interstices thereof. The secondary, stiffening impregnant may be introduced in the desired controlled amount into the dry, rubber-impregnated sheet, which, by virtue of its residual porosity, permits such secondary impregnation to be readily effected. In view of the fact that a welt-innersole need have high internal ply adhesion to the extent of only about one-half its thickness, that is, up to or slightly beyond the plane where channeling leaves off, the artificial leather made in accordance with the present invention may be cemented as by latex or rubber cement to an artificial leather made as ordinarily from a water-laid felt and latex and having considerably lower internal ply adhesion. The ordinary artificial leather backing thus plied therewith enhances its quality of stiffness, because a waterlaid felt conduces, with a given rubber usage, to a stiffer artificial leather than does a felt formed in a dry way. Shoe innersoles made from the artificial leathers of the present invention may be channeled and otherwise satisfactorily processed by the usual welt-innersole machines used in connection with genuine leather. They are eminently fitted for service in a shoe even when the coagulant is not previously removed therefrom, as by washing, since the coagulant may be used in such small amount and may be so mild as to have little, if any, effect on the stability of the ultimate article or upon the foot.

There are various rubber-coagulants available for the purposes of the present invention, but, in any event, one must use water-soluble coagulants, such as acid salts or neutral salts which hydrolyze in water to afford an acid condition. Of various such salts, including alum, magnesium sulphate, magnesium chloride, or the like rubber-coagulants, which might be employed in accordance with my invention, I prefer to use magnesium chloride because it is a mild chemical but a highly effective rubber-coagulant. The simplest way to effect a substantially uniform distribution of the coagulant through the fibrous raw material is to apply it as an aqueous solution to the material, then to dry the solution-impregnated material, and finally to condition it for the dry-felting operation, as hereinbefore described. It is, however, possible to reduce the rubber-coagulant to the form of an impalpable powder, which may then be uniformly scattered throughout the fibrous material before, during, or after its conditioning for the dry-felting operation. The impregnation of the material with a solution of the coagulant followed by drying, however, ensures a fixation or deposition of the coagulant as crystals 115 on all the fiber surfaces so that coagulation of the latex takes place more smoothly and uniformly in the web formed from the dry material. Apparently, the latex spreads uniformly throughout the dry web before the crystals of coagulant 120 have gone into solution inthe latex water to such an extent as to exercise much coagulating effect and thereby to impede uniform impregnation of the web with the latex. After the latex has entered uniformly into and throughout the web, the coagulant acts so quickly that even when the web proceeds to the drier immediately after impregnation, thickening or coagulation is completed before drying has proceeded to any substantial degree, wherefore there is but little rubber in colloidal particle form to migrate to the surface of the web during the drying operation.

In view of the fact that the webs of the present invention. are formed in a dry way, as distinguished from -so-called water-laid webs or felts which are prepared through the deposition of fibers from aqueous suspension on machinery of the papermaking type, I shall, for convenience of designation, refer in the appended claims to my webs or felts as dry-laid webs or felts. The quoted expression is used in a comprehensive sense to embrace webs formed in a dry way from fibrous material, irrespective of the particular type of machine employed for integrating or uniting the fibers into a coherent layer or mass.

The term latex is used in the appended claims in a comprehensive sense to include not only those latices purchased on the open market containing merely ammonia or other preservatives or stabilizing agents, but also latices which have been 150 specially treated or compounded, for instance,

vulcanized latices; latices compounded with vulcanizing ingredients, such as sulphur, accelerators tially uniformly distributed therethrough a rubher-coagulant.

2. As a step product, a coherent, substantially dry, dry-laid web of fibers containing substantially uniformly distributed therethrough a'rubber-coagulant fixed to the fibers.

3. As a step product, a coherent, substantially dry, dry-laid web of fibers containing substan-.

tially uniformly distributed therethrough a rubber-coagulating salt crystallized on the surfaces of the fibers.

4. As a step product, a coherent, substantially dry, dry-laid'web of fibers containing substantially uniformly distributed therethrough mag(- nesium chloride.

5. As a step product, a coherent, substantiall dry, dry-laid web of fibers containing substantially uniformly distributed therethrough only about 1% by weight of magnesium chloride.

6. An artificial leather comprising a dry-laid web of fibers containing distributed therethrough a rubber-coagulant and impregnated throughout with rubber coagulated from latex in situ in said web by said coagulant.

7. An artificial leather comprising a dry-laid web of fibers containing distributed therethrough a rubber-coagulating salt and impregnated throughout with rubber coagulated from latex in situ in said web by said salt.

8. An artificial leather comprising a dry-laid web of fibers containing distributed therethrough magnesium chloride and impregnated throughout with rubber coagulated from latex in situ in said web by said magnesium chloride.

9. An artificial leather comprising a dry-laid web of fibers containing distributed therethrough a rubber-coagulant and impregnated throughout with rubber coagulated in situ in said web by said coagulant,said rubber phase being enveloped by a stiffening impregnant.

10. An artificial leather comprising a dry-laid web of fibers containing distributed therethrough a rubber-coagulant and impregnated throughout with rubber coagulated in situ in said web by said coagulant, said rubber phase being enveloped by an impregnating phase of resinous stiffening agent.

11. An artificial leather comprising a dry-laid web of fibers containing distributed therethrough a rubber-coagulant and impregnated throughout with rubber coagulated in situ in said web by said coagulant, said rubber phase being enveloped by an impregnating phase of thermoplastic stiffening agent.

12. A two-ply artificial leather comprising a: dry-laid web of'fibers impregnated with rubber bonded to a waterlaid web of fibers impregnated with rubber..

l3.'A two-ply artificial leather comprising a dried, latex-impregnated, water-laid web of fibers bonded to a dry-laid web of fibers impregnated throughout with rubber coagulated from latex in situ in said web by a rubber-coagulant.

14. A process which comprises distributing a rubber coagulant substantially uniformly throughout fibrous material, forming said fibrous material in a dry way into a coherent web, im pregnating said web with latex, and drying said impregnated web.

15. A process which comprises treating fibrous material with an aqueous solution of rubber-co agulant, drying said fibrous material, forming said fibrous material in a dry way into a coherent web, impregnating said web with latex, and drying said impregnated web.

16. A process which comprises incorporating a rubber-coagulant into'woodpulp, individualizing the wood pulp fibers, forming said fibers in dry condition into a coherent web, impregnating the web with latex, and drying the impregnated web.

1'7. A process which comprises treating wood pulp with an aqueous solution of a rubber-coagulant, drying the wood pulp, individualizing the wood pulp fibers, forming said fibers in dry condition into a coherent web, impregnating the web with latex, and drying the impregnated web.

18. A process which comprises distributing a rubber coagulant substantially uniformly throughout wood pulp, individualizing the wood pulp fibers, depositing said fibers in dry condition from suspension inair into a fiufiy web, compacting the web, impregnating the compacted web with latex, and drying the impregnated web.

19. A process which comprises treating wood pulp with an aqueous solutionof a rubber-coagulant, drying the pulp, individualizing the wood pulp fibers, depositing said fibers in dry condition from suspension in air into a fluffy web, compacting'the web, impregnating it with latex, and drying the impregnated web.

20. In a process of making sheet material from fibrous material and a coagulatable aqueous dispersion of water-immiscible material, those steps which comprise distributing a coagulant for said aqueous dispersion substantially uniformly throughout the fibrous material, forming said fibrous material in a dry way into a coherent web, impregnating said web with said aqueous dispersion of water-immiscible material, and

drying said impregnated web. 

